1. Field of the invention
This invention relates to sealing rings for fluid conduits and more particularly to leasing rings incorporating electrochemical sensing electrodes.
2. Brief Description of the Prior Art
Electrochemical measurements relating to fluids contained inside sealed containers or piping systems would be of value to determine the properties of the fluids and to detect changes in the properties of the fluid that might indicate corrosion of the container or pipes. Such measurements require an electrochemical sensing electrode in contact with the solution within the sealed system. Such contacts could be provided by a simple through-wall fitting that supports an electrochemical electrode in contact with the fluid and provides an insulated electrical conductor extending through the wall of the fluid containment vessel.
In most circumstances, however, the use of conventional through-wall fittings is disadvantageous and ineffective. In the case of fluid handling systems that must be of the highest integrity, e.g., in nuclear reactor facilities or in naval vessels such as submarines, it is preferred to have as few apertures as possible in the fluid handling systems because each such aperture is considered a weak point that may compromise the integrity of the system. Furthermore, special elements with electrochemical fittings introduce complexity into the system because, e.g., a special pipe segment incorporating such a fitting must be installed, and inventories of such special pipe segments must be maintained.
Another situation in which a conventional through-wall electrode fitting is disadvantageous is in the sensing of crevice corrosion that may be occurring within the fluid handling system. Crevice corrosion occurs in liquid-filled small cracks in the metallic components of the fluid handling system or in the fluid-filed interstices that occur in the couplings between parts of the system, e.g., at flanged pipe joints. Such corrosion afflicts even alloys that are highly resistant to corrosion in bulk, e.g., stainless steel or the Inconel.RTM. series alloys. Furthermore, because the crevice corrosion phenomenon is not well understood, it is difficult to predict when and where it will occur. At present, the only reliable method of detecting crevice corrosion is periodic inspection of the fluid handling system, which ordinarily requires draining and disassembly. In view of the great expense entailed by such inspection, alternative methods of detecting crevice corrosion have been sought. It has been found that corrosion at the surface of a metallic member immersed in a fluid can be detected electrochemically by monitoring the complex electrical impedance between the surface of the article to be inspected and a test electrode located in the fluid close to that surface. Such measurements have become conventional for monitoring corrosion in research. They can also be used to detect crevice corrosion, but the electrode must be located close to the location at which the crevice corrosion is occurring. Accordingly, to detect crevice corrosion occurring at flanged joints incorporating a sealing ring (O-ring) where the corrosion may be occurring in the narrow regions where the sealing ring is compressed against the face of the flange, it would be necessary to provide special flanges with fittings for mounting an electrode in contact with the thin layer of fluid found between the flanges. The design and implementation of such fittings adds considerable complexity and expense to the fluid handling system. The extra fitting is also a potential place for leakage, and, in fact, introduces another discontinuity in the wall of the system which may itself be a location for crevice corrosion.
Accordingly, a need has continued to exist for a simple means of inserting an electrode into a sealed fluid handling system, e.g., a piping system, in close proximity to locations in the piping system that are subject to crevice corrosion.